Given a rosette fetal screen indicating 1 rosette/3 fields, what does it imply for an Rh-negative mother with an Rh-positive child?

The finding of 1 rosette in 3 fields during a rosette fetal screen indicates a small amount of Rh-positive fetal blood has entered the maternal circulation. This is significant for an Rh-negative mother who has given birth to an Rh-positive child because it suggests fetal-maternal hemorrhage has occurred.

In practice, for an Rh-negative mother, the standard protocol is to administer Rh immune globulin (RhIg) to prevent the development of anti-D antibodies that could affect future pregnancies. The amount of RhIg needed is determined by the extent of fetal-maternal hemorrhage.

A rosette screen that shows 1 rosette in 3 fields typically indicates that the hemorrhage is not large enough to require quantification, which would be necessary if the rosettes were more numerous, indicating a larger amount of fetal blood in the maternal circulation. Therefore, the general guideline is to provide one vial of Rh immune globulin for less pronounced instances of bleeding detected by this screening process. Hence, the correct choice reflects the appropriate standard of care for this scenario, suggesting that the mother needs 1 vial of Rh immune globulin due to the detected level of Rh-positive cells.